Acquisitions and Divestitures 2013 Divestiture of Anadarko Assets (Details) (USD $)	0 Months Ended	12 Months Ended
	Aug. 01, 2013	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property		$ (1,508,000)		$ (51,000)		$ (1,000)
Revenues discontinued operations [Abstract]
Transportation and treating		4,020,000		4,186,000		3,923,000
Total revenues from discontinued operations		4,020,000		4,186,000		3,923,000
Cost and expenses discontinued operations [Abstract]
Transportation and treating		1,207,000		1,306,000		912,000
Drilling and production		(18,000)		463,000		1,142,000
Depletion, depreciation and amortization		627,000		2,577,000		2,247,000
Impairment expense		0		0		243,000
Total costs and expenses from discontinued operations		1,816,000		4,346,000		4,544,000
Non-operating expense, net		0		(1,000)		(39,000)
Income (loss) from discontinued operations before income tax		2,204,000		(161,000)		(660,000)
Income tax (expense) benefit		(781,000)		54,000		238,000
Income (loss) from discontinued operations—basic and diluted		1,423,000		(107,000)		(422,000)
Andarko Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property		3,200,000
Consideration net of transaction costs	428,300,000
Revenues discontinued operations [Abstract]
Total revenues from discontinued operations		59,631,000		84,616,000		103,746,000
Cost and expenses discontinued operations [Abstract]
Expenses		46,357,000	[1]	89,602,000	[1]	80,308,000	[1]
EnerVest | Andarko Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration from asset divestiture	400,000,000
Other Third Parties | Andarko Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration from asset divestiture	38,000,000
Oil and Gas Properties | Andarko Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration from asset divestiture	$ 388,000,000

[1] Expenses include lease operating expense, production and ad valorem tax expense, accretion expense and depletion, depreciation and amortization